1. Field of the Invention
The invention relates to a process for feeding suspended solid or fluid carbonaceous materials into reactor spaces operating under pressure: solid particles optionally mixed with a suspending agent, binding agent or solid or liquid lubricant, not easily pumpable suspensions, pasty or viscous stocks, melts and the like, as a plug of compressed feed material which is impervious at the pressure predominating in the reactor and is continuously renewed as it enters the latter as a strand of feed material by means of at least one rotatable screw conveyor in a closely fitting housing, and a device for carrying out such a process.
2. Background of the Related Art
Processes for continuous feed of solid fuels into a gasification reactor by means of a twin-screw extruder are described in DE 27 21 047 C3 and also EP 0 065 459 A3.
A proven system for solid feed into a pressure gasification unit is the feed of the solid as a suspension with the use of special pumps (see U.S. Pat. No. 3,607,157). Another possibility is the dry feeding of solid fuel by use of pressure locks, cf. DE 28 56 617 C3.
Feeding with a suspension pump requires a comparatively great amount of added liquid, which limits of the attainable composition of synthesis gas with water as added liquid. Additional devices such as mixers, stirred receiving vessels and circulating pumps are necessary to prepare the solid-liquid suspension and keep it homogeneous.
So-called slurry presses are used for feeding of coal slurry into high-pressure apparatus for coal liquefaction in slurry phase hydrogenation, cf., W. Kroenig, "Die katalytische Druckhydrierung von Kohlen, Teeren und Mineraloelen" [Catalytic pressure hydrogenation of coals, tars and crude oils], Springer-Verlag, Berlin/Goettingen/Heidelberg, 1950, p. 228 ff.
Bergius had already pressed coal mixed with oil, to form a very thick cold paste which was transported by a screw conveyor to the "slurry press", which brought it to the operating pressure and carried it as a cold strand into the high-pressure furnace (cf. W. Kroenig, loc. cit., p. 38).
Therefore, a key component for the operability of processes for conversion or manipulation of materials under high pressure is the system used for feeding of the materials or mixtures of materials into the corresponding reactor spaces operated under pressure, since the materials or mixture of materials must be conveyed against the often very high pressures in the interior of the pressure spaces and at the same time discharge or backfiring of hot and reactive high pressure process gases often present in this type of processes must be reliably avoided. Typical examples for such type of processes are the gasification of carbonaceous materials in the refractory lined reaction zone of free-flow noncatalytic unpacked partial oxidation synthesis gas reactors or the catalytic pressure hydrogenation in slurry phase of carbonaceous materials.
A suitable device in the form of at least one screw conveyor, rotatable in a closely surrounding housing, for the introduction of solid fuels into a pressure gasification reactor is described in DE 28 50 121 C3.
For expert thinking relative to the introduction of materials or mixtures of materials in the form of solid particles, optionally mixed with a suspending agent or binding agent or not easily pumpable suspensions, pasty or viscous stocks, melts and the like, refer to, among others, W. Wiedmann and W.A. Mack, "The Use of Twin Screw Extruders for Feeding Coal Against Pressures of up to 1500 psi," Proceedings of the Conference on Coal Feeding Systems held at the California Institute of Technology, Pasadena, Calif., June 21-23, 1977. According to this publication, uniformly rotating twin screw extruders are especially suitable because of their feed and conveying behavior, the favorable wear behavior, and the self-cleaning capability of the partially or completely meshing twin screw system.
With the use of a screw extruder as the introduction system into a free-flow partial oxidation gasification reactor, the solid must be introduced into the gasification reactor with a highly constant flow rate. Disturbances of the solid fuel feed into the gasification reactor can lead to momentary initiation of combustion of the present synthesis gas with the oxygen containing gases charged to the gasification reactor. The consequences of such trouble are suddenly rising gasification temperatures and a great danger to the refractory lined reaction zone of the gasification reactor.
With the use of an extruder for feeding against pressure of the carbonaceous charge material into the reactor for free-flow partial oxidation, the liquid and inert gas ballast can be considerably reduced. The charge stock is introduced at the upstream end of the extruder, driven dowstream by the rotation of the screw(s) and mixed with a liquid or solid lubricant, for example, water or oil. The proportion of this binding agent is smaller than the amount required for the suspension process. The binding agent and solid are mixed to a homogeneous paste in the mixing zone of the extruder. In the pressure buildup area of the extruder the solid is brought to a pressure above the reactor pressure by formation of a plug of compressed charge material which is impervious at the pressure predominating in the reactor and is continuously renewed as it enters the latter. After entry in the pressure reactor space the strand of carbonaceous charge material is conveyed through a nozzle in the so-called delivery head and disagglomerated and disintegrated by one or more gas or liquid jets and pneumatically conveyed into the reaction space, where, for example, after addition of a gasification agent such as gaseous oxygen, oxygen containing gases or air, partial oxidation which can be made up to synthesis gas takes place, or after addition of hydrogen under the typical conditions of slurry-phase hydrogenation, liquefaction takes place to recover useful products.
Since the mixing, conveying and pressure buildup take place in the extruder, other related peripheral equipment is eliminated. The reliability of the introduction system achieved with an extruder, however, is more problematic because of existing conditions, since the seal between the pressure space of the reactor and the upstream side of the system is achieved only by the dynamically acting solid plug of carbonaceous charge material, which is impervious at the pressure in the reactor.